1. Field of the Invention
This invention relates to a light emitting device with a light emitting element on the surface of which a high refractive index layer is formed.
2. Description of the Related Art
Light emitting devices are conventionally known in which a light emitting element such as an LED (=light emitting diode) is sealed with a transparent resin material such as epoxy resin. In this kind of light emitting device, since the surface portion (or a surface layer located on light extraction surface side thereof) of the light emitting element has a refractive index higher than that of the transparent resin material, a range of angle is defined within which the condition of total reflection can be satisfied at the interface of the light emitting element and the sealing material. It is impossible to extract a light emitted from the inside of the light emitting element and entering into the interface at an angle within that range of angle.
JP-A-10-65220 discloses a light emitting device with improved light extraction efficiency. In this light emitting device, the periphery of the light emitting element is sealed by a first resin such as polyvinylcarbazole, and the outside of the first rein is sealed by a second resin with a refractive index lower than the first resin. The light extraction efficiency of light emitted from the light emitting element can be enhanced as compared to the case where the light emitting element is sealed by only epoxy resin.
JP-A-2003-243727 discloses a light emitting device that a coating layer including phosphor particles therein is formed on the surface of the light emitting element. The phosphor particles are operable to convert a part of light emitted from the light emitting element, where light emitted from the light emitting element is combined with the converted light radiated from the phosphor particles to produce white light. The coating layer further includes fine particles of a transparent inorganic material so as to improve the emission characteristics of the device, where it has a region with the thick fine particles and a region with the thin fine particles formed therein.
However, the light emitting device of JP-A-10-65220 still retains the range of angle to satisfy the condition of total reflection since the first resin covering the periphery of the light emitting element is lower in refractive index than the surface portion of the light emitting element. Thus, the device of JP-A-10-65220 is insufficient in light extraction efficiency.
The light emitting device of JP-A-2003-243727 has the region with the thin fine particles on the periphery of the light emitting device, where the amount of the fine particles significantly lowers to allow the surface of the light emitting element to be covered with the resin sealing material which causes a reduction in light extraction efficiency. Thus, the device of JP-A-2003-243727 is not intended to improve the light extraction efficiency from the light emitting element.